From the manufacturer (Exaclair Inc., makers of Clairefontaine and Quo Vadis stationery lines): “The orange notebook with a cult following! They are a favorite of artists, designers, architects, scientists and people who like to use graph paper for notes, sketching and hand drafting. The bright orange covers are scored near the top to fold neatly behind the pad while writing…. The orange cover dates back to the 1930s. It remains unchanged to this day.”
These lovely French writing pads are simple perfection: a variety of sizes, nice paper with blank, ruled, or lined options, and the classic golden cover.
I use the No. 16 (5.75″x8.25″, top staple, lined) for recording my teaching notes. It’s professional enough to use in front of my students, and well-made enough for my taste (no Five-Star wire-bound crap for me, thank you very much). I find that a page a day fills my planning and note-taking needs.
Rhodia pads are available through Vickerey, which would be a good place to get them, as ordering from the manufacturer is complicated and French. Of course, your local stationery shop or university bookstore is likely to have them in stock.
edit: these aren’t technically notebooks, they’re pads. Thanks for pointing it out!